As a communication device implementing an Adaptive array Antenna System (AAS), a communication device using a multiple input multiple output (MIMO) has been proposed (for example, refer to Patent Literature 1).
Also, as a transmission method of the AAS communication device, a method of selecting an AAS method and a MIMO method has been proposed (for example, refer to Patent Literature 2). This method estimates the orthogonality of a channel characteristic between transmission and reception antennas to determine and switch which of the adaptive array antenna system and the MIMO has an advantage. Also, Patent Literature 2 discloses an example of a base station and propose a transmission method for a downlink.
In the communication device using the MIMO, a method of using a channel characteristic H between transmission and reception antennas has been known. For example, a Zero Forcing (ZF) equalization method and a Minimum Mean Square Error (MMSE) equalization method are examples of the method of using the channel characteristic H.